First responders such as fire fighters, police officers, and search and rescue teams are subject to numerous dangers. A significant contributor to these dangers is the potential of being lost or disoriented within a building that is filled with smoke and collapsed structures.
Radio Frequency (RF) based tracking systems rely on a combination of fixed beacons and mobile tags to track the movement of the tags, based on signal strength or time-of-flight measurements of specific RF signals. Near-continuous RF links with the beacons are necessary for the system to calculate timely location information. However, RF propagation variability may result in loss of path data for a mobile tag or tags. An alternative approach, which overcomes the RF link variability issue, employs a dead-reckoning module (DRM) in each mobile tag. The DRM can contain multiple sensors, such as altimeters, barometers, accelerometers, temperature sensors, and compass sensors, for example. The RF link is then used solely for data communications between the mobile tags and the base stations.
However, determining the absolute location of each mobile tag would require a known frame of reference within which the mobile tags are used. The cost of such a frame of reference would be prohibitive, needing a high density of beacons for RF tag tracking or adding GPS capability to the DRM. Moreover, both the RF and the DRM approaches have error sources which exhibit cumulative effects such as multi-path in the RF tags and sensor drift.
Movement, or failure, of receivers may degrade the accuracy of the position location information. Specifically, the use of RF tracking systems to monitor persons, such as first responders, may encounter a catastrophic event such as a building collapse, leading to the effective re-location of one or more of the receivers. In this case the reported tag location will be corrupt due to the displacement of the receivers and subsequent apparent co-location of a tag near multiple receivers.
One of the problems with systems that calculate the location of an individual using a plurality of signals is that some signals may be less representative of the actual location than others. Prior art systems do use signal strength to determine location from multiple anchors.
It would be of advantage in the art if a system could be devised that would permit the use of an array of fixed beacon receivers that would maintain their utility even when moved due to outside influences such as damage to the place where the beacon receivers are fixed such that the calculations of signal strength could be weighted to favor those signals of maximum confidence.
Yet another advantage would be if a tracking tag could be developed that would allow integration of DRM data that is weighted to use signals that have maximum confidence factors.
Still another advantage would be if errors arising from multiple RF transmissions could be compensated for by weighting the respective signals.
Other advantages will appear hereinafter.